Hypertensive and Normal Pregnancy--Calcium Metabolism and Renin-Angiotensin - SCOR in Hypertension

BACKGROUND:

Beginning in Fiscal Year 1975, the multidisciplinary SCOR examined causes, consequences, and treatments of human hypertension. A central theme was the renal basis for human hypertension. The subproject on calcium metabolism and the renin-angiotensin system in hypertensive and normal pregnancy began in December, 1990.

DESIGN NARRATIVE:

A longitudinal study was performed on normal pregnant women and women with chronic hypertension who had a high incidence of superimposed preeclampsia. In a previous study, the investigators had demonstrated that preeclampsia was associated with reduced urinary excretion of calcium and with lower plasma renin activity (PRA) compared with normal pregnancy. The goal of the investigators was to identify the metabolic and cellular basis for these alterations in calcium homeostasis and in the renin angiotensin system. They tested two hypotheses. The first hypothesis was that diminished placental and/or renal production of 1,25-dihydroxyvitamin D, leading to lower serum calcium, higher parathyroid hormone, and increased renal tubular reabsorption of calcium, was the metabolic basis for hypocalciuria in preeclampsia. The second hypothesis was that lower PRA in preeclampsia was due to systemic and renal vasoconstriction with hypertension and diminished natriuresis.

Serial measurements of 1,25-dihydroxyvitamin D, parathyroid hormone, serum ionized calcium, PRA, estradiol and progesterone, and urinary calcium and electrolytes were obtained, particularly at the onset of preeclampsia. Acute renal hemodynamic studies were also performed in women with preeclampsia and in gestational age matched normals. The studies investigated the relationships among glomerular filtration rate, renal blood flow, parathyroid hormone, vitamin D, atrial natriuretic factor, renin, estradiol and progesterone, and sodium and calcium excretion during infusion of inulin and PAH with either saline or calcium chloride.